Many contemporary philosophers agree that Karl Popper (1902–1994) was one of the most influential 20th-century thinkers in their field. Most of them, in turn, would contend that the field of science has never been the same since Popper introduced the notion of fallibilism. Clunky though this word is, its insight is profound, namely that science advances not through the effort to prove a theory but instead by doing one’s darndest to disprove it.

Crucially, Popper’s theory was not limited to the world of scientific discovery. It also spilled into political theory, a field he felt compelled to turn to in the mid-1930s. As a 30-something Jewish academic living in interwar Vienna—albeit one whose family had converted to Lutheranism—Popper had grown increasingly anxious over the seemingly irresistible rise of totalitarian states. Less than a year before Nazi Germany’s annexation of Austria, Popper and his wife, Hennie—who hammered out her husband’s drafts on a creaking typewriter—left for Christchurch, where he took a teaching position at the University of New Zealand.

Though exiled to a far-flung corner of the New World, he could not help but dwell on the forces now tearing apart the Old World. In his effort to analyze the logic of totalitarianism, Popper came to the realization that when it came to the ideologies of his own age, there was little new under the sun. Even totalitarianism, an ideology rendered yet more terrifying by advances in science and technology, was not sui generis. Instead, its intellectual roots stretched back to antiquity and, of all thinkers, to Plato. In his massive The Open Society and Its Enemies—published just before his return to Europe in 1945—Popper in effect identifies Plato not just as the father of western philosophy, but also the father of the forces that had wrought the gulags and the gas chambers.

This assertion still shocks. After all, if you were to construct a baseball lineup of the western world’s foundational thinkers, Plato would almost certainly bat cleanup. Yet Popper, poring over the Republic as the world burned, was on to something disturbing about the ancient Athenian’s worldview. And he cared not a whit for Plato’s hallowed reputation; icons be damned. “I consider the destruction of the awe of the Great Names, the Great Intellectual Authorities,” he declared to a friend, “one of the necessary prerequisites of a recuperation of mankind.”

Popper lambastes Plato for inventing a rigidly stratified state, a purified tribal society preferable to the Athenian democracy into which he was born. It is composed of three classes: the guardians, their troops, and the workers. Ruling over this ideal republic were philosopher-kings, who pedaled “noble lies” that justified a hierarchy of social classes. If human beings believed that they were made of different metals—their station in life determined by how much gold, silver, iron, or brass was within them—they would not only accept the stratification of the classes but also care for one another and for the state. Thus could the self-described best and brightest maintain their power by sheer force and fantasy; the poets, whose tales might reveal the injustices and insanities of the Republic, would be banished.

Tellingly, Plato admits that the lowest class, whom he refers to as the “sheep,” would fear, for good reason, the guardians, who might well “act as wolves rather than dogs.” No less tellingly, these noble lies anticipate the pseudoscientific lies informing the genocidal ideologies of the 20th century that divided peoples into superior and inferior races. By war’s end, when Popper was trying to find a publisher for Open Society and Its Enemies, he began to take the tragic measure of such insanities; 16 members of his own family were consumed in the furnaces of the death camps. Having drafted the book during this grim period, Popper confessed, “may help explain why some of its criticism strikes me as more emotional and harsher in tone than I could wish.”

He was right on this score. Impatient and imposing, Popper did not suffer fools easily—a category, unhappily, under which he lumped most everyone who disagreed with him. (Popper’s students referred to his book as The Open Society By One of Its Enemies.) But there is also no doubt that Popper was right about the implications of Plato’s proposed republic. The elaborate blueprint, Popper insisted, came down to one thing: the effort to “arrest all change.”

Arrest all change: This is the lasting mark not of an open society, but instead a closed one. The former thrives on what Popper calls a “critical attitude,” one that reflects the principle of fallibilism: Truths are only true if they are verified through the give and take of experience and experiment. The latter, however, throttles such practices, preferring the “dogmatic” power of myths that maintain the stability of the state and the submission of its citizens.

Popper acknowledged that his interpretation of Plato was only that: his interpretation. There are, of course, many other interpretations of Plato far less dark and far more generous. After all, Plato’s work is not polemical; apart from his last works, Plato crafted dialogues, conversations in which Socrates engages with others on the perennial questions that make our lives meaningful. More simply, as Allan Bloom wrote in his introduction to the Republic, the dialogues function as “a living teacher who makes his students think.”

This was the vocation of Socrates and, ideally, remains the vocation of many who instruct students today. Yet Socrates, famous for his use of irony, would no doubt enjoy efforts of present-day guardians—such as the administrators at Texas A&M who recently banned Plato’s Symposium because of its discussion of gender—who are trying to censor his own words in their effort to arrest all change. Socrates famously said that the unexamined life is not worth living. Yet for the ancient Athenian, such an examination was possible only through dialogue, an activity that led to Socrates’s death, after he was charged with the crime of impiety for corrupting the city’s youth.

Popper had good reason to fear the fatal attraction that a closed society exercised on those who aspired to be the kings and guardians wielding untrammeled power. But crucially, he also feared the same attraction such a society held for those who, fearful of the freedom that allows for the play of ideas and practices, wish to flee to the comfort of a world closed off from such activities.

In his book’s conclusion, Popper insists that history has no meaning. But this crotchety prophet refused to see this statement as a reason for despair, much less nihilism. To the contrary, Popper interpreted it is as a call to action. We can do more, he declared, than “look aghast at the history of political power,” or “look at it as a cruel joke.” To the contrary, we can interpret the past as the means to better “fight for an open society, for a rule of reason, for justice, freedom, equality, and the control of international crime.” Two millennia after Plato wrote his dialogues, nearly a century after the publication of The Open Society, the role of public dialogue remains as central as ever.